树状数组练习

先看一下最后一题，这是一个树状数组的题目，那就水一下吧,但是由于没有注意问题，wa了很多次

const int N = (int)1e5 + 5;
int n;
int flag[N];
int dp[N];
class Solution {
public:
    vector<int> countOfPeaks(vector<int>& nums, vector<vector<int>>& queries) {
        n = nums.size();
        memset(dp,0,sizeof dp);
        memset(flag,0,sizeof flag);
        vector<int> ans;
        for (int i = 1; i < n - 1; i++) {
            if (nums[i] > nums[i + 1] && nums[i] > nums[i - 1]) {
                flag[i + 1] = 1;
                add(i + 1, 1);
            }
        }
        //         for (int i = 1; i <= n; i++) {
        //     cout << i << " " << find(i) - find(i - 1) << endl;
        // }
        for (int i = 0; i < queries.size(); i++) {
            if (queries[i][0] == 2) {
                int index = queries[i][1], val = queries[i][2];
                nums[index] = val;
                fun(index, nums); fun(index - 1, nums); fun(index + 1, nums);
        //                 for (int i = 1; i <= n; i++) {
        //     cout << i << " " << find(i) - find(i - 1) << endl;
        // }
            }
            else {

                 //ans.push_back(find(queries[i][2]) - find(queries[i][1] + 2));
                 int temp = find(queries[i][2] + 1) - find(queries[i][1]);
                 if (flag[queries[i][2] + 1]) temp--;
                 if (flag[queries[i][1] + 1]) temp--;
                 ans.push_back(temp>0?temp:0);
            }
        }
        return ans;
    }

    int lowbit(int x) {
        return x & (-x);
    }
    void add(int x, int p) {
        for (int i = x; i <= n; i += lowbit(i)) {
            dp[i] += p;
        }
    }
    int find(int x) {
        if (x == 0) return 0;
        return dp[x] + find(x - lowbit(x));
    }
    void fun(int index, vector<int>& nums) {
        if (index <= 0 || index >= (n - 1)) return;
        if (nums[index] > nums[index + 1] && nums[index] > nums[index - 1]) {
            if (flag[index + 1]) return;
            add(index + 1, 1), flag[index + 1] = 1;
        }
        else {
            if (!flag[index + 1]) return;
            add(index + 1, -1), flag[index + 1] = 0;
        }
    }
};